1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to speed pattern generators for elevator systems.
2. Description of the Prior Art
The position of an elevator car may be determined by generating a distance pulse for each standard increment of car travel, such as a pulse for each 0.25 inch of travel, and by counting the pulses generated. The counter is set to a predetermined count at the lowest floor, and the count is incremented during up travel and decremented during down travel. The location of each floor of the associated building is stored in a suitable memory, in terms of a count value, using the standard increment. The position of the car may be compared with the location of a target floor, and when the count difference equals the desired slowdown distance, the slowdown phase of the run is initiated. The slowdown distance may be continuously maintained and decremented by the distance pulses, with the distance-to-go count being used to generate the slowdown speed pattern.
Theoretically, the slowdown speed pattern should be able to bring the car accurately to floor level. However, the distance pulses are usually detected by a pulse wheel driven by the traction sheave, or from the governor sheave. Slippage between the ropes and sheave grooves creates a mismatch between the actual car position and the position count, as does wear of the ropes and grooves. Thus, it is conventional to detect the actual presence of the elevator car when it reaches a predetermined landing distance from the target floor, and to switch from the normal speed pattern generator to an auxiliary speed pattern generator. This auxiliary or landing speed pattern generator is responsive to the absolute position of the elevator car relative to the target floor. Such an auxiliary speed pattern generator may develop a pattern from metallic plates disposed adjacent to each floor, which cooperate with electromagnetic windings carried by the elevator car. The metallic plates are shaped such that the pattern output voltage is reduced according to the actual position of the car relative to the target floor.
While the speed pattern transfer arrangement referred to above will stop the car accurately at floor level, it can produce a "bump" of sufficient magnitude that it is felt by passengers in the elevator car, if the mismatch between the normal slowdown speed pattern and the auxiliary or landing speed pattern exceeds a predetermined magnitude. The "bump" occurs as the speed error abruptly changes and the feedback control attempts to cause the car speed to change abruptly.